Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “POINT DEFECTS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

ESR study on the visible photocatalytic mechanism of nitrogen-doped novel TiO{sub 2}

The visible photocatalytic mechanism of nitrogen-doped novel TiO{sub 2} was studied by means of electron spin resonance spectroscopy (ESR). It was found that, under visible light irradiation, the concentration of single-electron-trapped oxygen vacancy (SETOV, V{sub o}{sup {center_dot}}) of novel TiO{sub 2} remained unchanged, but that of nitrogen-doped novel TiO{sub 2} increased and returned to original state when the light was turned off. This implies that, aside from V{sub o}{sup {center_dot}} in bulk of nitrogen-doped novel TiO{sub 2}, oxygen vacancy without trapped electron (V{sub o}{sup {center_dot}{center_dot}}) was formed on its surface. V{sub o}{sup {center_dot}{center_dot}} as a surface electron trap captured photogenerated electron from the bulk to generate extra V{sub o}{sup {center_dot}}, carrying out photocatalytic reaction on the surface. At the same time, nitrogen doping product NO was chemically adsorbed on the vicinity of V{sub o}{sup {center_dot}{center_dot}} and inhibited the attack of oxygen, allowing V{sub o}{sup {center_dot}{center_dot}} to remain stable in air. The synergistic action of the two kinds of active structures, i.e., bulk V{sub o}{sup {center_dot}}-NO-Ti and surface V{sub o}{sup {center_dot}{center_dot}}-NO-Ti, accounted for the visible photocatalytic activity of N-doped novel TiO{sub 2}. - Graphical abstract: Synergistic action is realized between (V{sub o}{sup {center_dot}}){sub bulk} and (V{sub o}{sup {center_dot}{center_dot}}){sub surf} in the presence of active structures (V{sub o}{sup {center_dot}}){sub bulk}-NO-Ti and (V{sub o}{sup {center_dot}{center_dot}}){sub surf} -NO-Ti. Research Highlights: > The origin of visible photocatalytic activity of the N-TiO{sub 2} was studied by ESR. > (V{sub o}{sup {center_dot}}){sub bulk} and (V{sub o}{sup {center_dot}{center_dot}}){sub surf} formed in N-TiO{sub 2}. > (V{sub o}{sup {center_dot}}){sub bulk} and (V{sub o}{sup {center_dot}{center_dot}}){sub surf} show a synergistic effect in visible photocatalytic. > TiO{sub 2} did not contain (V{sub o}{sup {center_dot}{center_dot}}){sub surf}, so no visible photocatalytic activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2010

Broadband magnetometry by infrared-absorption detection of nitrogen-vacancy ensembles in diamond

We demonstrate magnetometry by detection of the spin state of high-density nitrogen-vacancy ensembles in diamond using optical absorption at 1042 nm. With this technique, measurement contrast, and collection efficiency can approach unity, leading to an increase in magnetic sensitivity compared to the more common method of collecting red fluorescence. Working at 75 K with a sensor with effective volume 50x50x300 {mu}m{sup 3}, we project photon shot-noise limited sensitivity of 5 pT in one second of acquisition and bandwidth from dc to a few megahertz. Operation in a gradiometer configuration yields a noise floor of 7 nT{sub rms} at {approx}110 Hz in one second of acquisition.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Suppression of donor-vacancy clusters in germanium by concurrent annealing and irradiation

Diffusion of phosphorous and arsenic in germanium under in situ proton irradiation has been performed and analyzed with secondary ion mass spectrometry. Dopant profiles corresponding to proton-exposed regions exhibit a higher penetration depth and more pronounced box shape than profiles of nonexposed regions. Continuum theoretical simulations reveal that diffusion under irradiation is much less affected by inactive donor-vacancy clusters than diffusion under annealing only. The suppression of donor-vacancy clusters is caused by interstitials in supersaturation and vacancy concentrations close to thermal equilibrium. Concurrent annealing and irradiation have the potential to attain high active doping levels in Ge.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Analysis of the absorption spectra and spectral hole burning in zero-phonon lines of F{sup +}{sub 3} and N{sub 1} colour centres in LiF crystals

The temperature dependences and mechanisms of broadening of zero-phonon lines of F{sup +}{sub 3} (488 nm) and N{sub 1} (523 nm) colour centres in LiF crystals are investigated. The results obtained make it possible to determine the quadratic electronic-vibrational coupling constant for N{sub 1} colour centres. The experimental data on the spectral hole burning in zero-phonon lines of F{sup +}{sub 3} and N{sub 1} colour centres indicate that the latter are positively charged. (laser applications and other topics in quantum electronics)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Ferromagnetic order in silicon-manganese alloys with phase separation

A phenomenological model of high-temperature ferromagnetism in silicon-manganese alloys has been proposed taking into account phase separation in these alloys, where manganese-rich particles of the secondary phase (precipitate MnSi{sub 2-z} with z Almost-Equal-To 0.25-0.30) are formed inside a manganese-depleted matrix of almost pure silicon. Precipitate MnSi{sub 2-z} is considered as the silicide MnSi{sub 1.7} containing a certain number of magnetic defects whose origin is due to the presence of weakly hybridized 3d orbitals of manganese. The silicide MnSi{sub 1.7} is a weak band ferromagnet in which strong fluctuations of the spin density (paramagnons) are present at a temperature much higher than its Curie temperature. It has been shown that the ferromagnetic exchange interactions between the magnetic moments of defects in precipitate exists due to thermal excitations of the spin density and the ferromagnetic order can appear at a temperature much higher than the Curie temperature of the silicide. The spatial structures and characteristics of this order have been described in the framework of the proposed approach for both homogeneous bulk precipitate and precipitate particles of various shapes and sizes. The short-range magnetic order near the bulk phase transition has been analyzed taking into account inhomogeneities in the distribution of magnetic defects in precipitate. The experimental data on the magnetic properties of silicon-manganese alloys have been interpreted in terms of the theoretical results obtained in this work.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Tailoring Kinetics on a Topological Insulator Surface by Defect-Induced Strain: Pb Mobility on Bi 2 Te 3

Heteroepitaxial structures based on Bi2Te3-type topological insulators (TIs) exhibit exotic quantum phenomena. For optimal characterization of these phenomena, it is desirable to control the interface structure during film growth on such TIs. In this process, adatom mobility is a key factor. We demonstrate that Pb mobility on the Bi2Te3(111) surface can be modified by the engineering local strain, ε, which is induced around the point-like defects intrinsically forming in the Bi2Te3(111) thin film grown on a Si(111)-7 × 7 substrate. Scanning tunneling microscopy observations of Pb adatom and cluster distributions and first-principles density functional theory (DFT) analyses of the adsorption energy and diffusion barrier Ed of Pb adatom on Bi2Te3(111) surface show a significant influence of ε. Surprisingly, Ed reveals a cusp-like dependence on ε due to a bifurcation in the position of the stable adsorption site at the critical tensile strain εc ≈ 0.8%. This constitutes a very different strain-dependence of diffusivity from all previous studies focusing on conventional metal or semiconductor surfaces. Kinetic Monte Carlo simulations of Pb deposition, diffusion, and irreversible aggregation incorporating the DFT results reveal adatom and cluster distributions compatible with our experimental observations.

Chemistry↗
DOE OSTI2010

Free energy reconstruction from steered dynamics without post-processing

Various methods achieving importance sampling in ensembles of nonequilibrium trajectories enable one to estimate free energy differences and, by maximum-likelihood post-processing, to reconstruct free energy landscapes. Here, based on Bayes theorem, we propose a more direct method in which a posterior likelihood function is used both to construct the steered dynamics and to infer the contribution to equilibrium of all the sampled states. The method is implemented with two steering schedules. First, using non-autonomous steering, we calculate the migration barrier of the vacancy in Fe-{alpha}. Second, using an autonomous scheduling related to metadynamics and equivalent to temperature-accelerated molecular dynamics, we accurately reconstruct the two-dimensional free energy landscape of the 38-atom Lennard-Jones cluster as a function of an orientational bond-order parameter and energy, down to the solid-solid structural transition temperature of the cluster and without maximum-likelihood post-processing.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2011

UV Spectra of Amino Acid Immobilized at Nanoparticles Formation through Nanosphere Lithography (NSL) by Plasma Treatment

The modifying of nanospheres structures by plasma treatments to the fabricated nanoparticles arrays by Nanosphere Lithography (NSL) techniques to create Periodic Particles Arrays (PPAs) with different size, shape and orientation. Spectra of amino acid that immobilized to the nanoparticles arrays under Ultra Violet (UV) spectrums were studied. The PPAs with different sizes, shapes and orientation were fabricated by plasma treatment of 5 sec, 7 sec and 10 sec to the Polystyrene Nanosphere (PSN). Plasma treatment will effect to the PSN including etching part of the PSN to produce a much bigger channel to the single layer template of the PSN. Metal was deposited at interstitial sites between of the polymer balls and later removed by dissolving them in organic solvent, leaving a hexagonal pattern of metal structures at the interstitial sites. The nanoparticles immobilized with the standard amino acid, which later investigated under UV spectrums. The spectrums shows the possibilities use as biosensor devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

A large polarization in Ce-modified bismuth ferrite thin films

Bi{sub 0.95}Ce{sub 0.05}FeO{sub 3} (BCFO) thin films were grown on SrRuO{sub 3}/TiO{sub 2}/SiO{sub 2}/Si(100) substrates via radio frequency sputtering. The BCFO thin film has a (111) orientation with a high phase purity. Improved dielectric behavior is observed for the BCFO thin film as compared with that of pure bismuth ferrite thin film. A large remanent polarization of 2P{sub r} {approx} 183.9 {mu}C/cm{sup 2} is induced in the BCFO thin film, owing to the (111) orientation and the introduction of Ce. The local phase decomposition induced by larger depolarization fields and the oxygen vacancies dominates the fatigue resistance of the BCFO thin film.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Advanced Thermoluminescence Spectroscopy as a Research Tool for Semiconductor and Photonic Materials: A Review and Perspective

Thermoluminescence (TL) or thermally stimulated luminescence (TSL) spectroscopy is based on liberating charge carriers from traps in the bandgap by providing enough thermal energy to overcome the potential barrier of the traps. It provides a powerful tool to measure the positions of the localized states/traps in the bandgap. Despite that, its applications in semiconductors are very limited. Herein, the basics of TL spectroscopy and the recent advances in the technique with focus on cryogenic thermally stimulated photoemission spectroscopy (C‐TSPS) which extends TL measurements to cryogenic regime and allows the detection of very low concentrations of shallow and deep localized states is discussed. One goal herein is to introduce the reader to the use of TL and C‐TSPS in the characterization of semiconductors, explaining how it can be applied and demonstrating its advantages as a powerful tool for measuring shallow donor/acceptor ionization energies in semiconductors and as a method for characterizing compensating defects. The article also discusses interesting potential applications of C‐TSPS in new research areas such as corrosion and formation of oxide layers on metal surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Impact of Laser Radiation on Microhardness of a Semiconductor

It was found that strongly absorbed Nd:YAG laser radiation leads to a non-monotonous dependence of microhardness of p- and n-type Si crystals on laser radiation. This dependence is characterized by two maxima for p-Si and one maximum for n-Si crystals. In both cases the increase of microhardness at higher laser intensity is explained by formation of mechanically compressed layer at the irradiated surface due to concentration of the interstitial atoms of Si at the surface in temperature gradient field. The decrease of the microhardness is explained by formation of nano-cones as a result of plastic deformation of the mechanically stressed layer. The additional maximum at lower laser intensity for p-Si crystal is explained by p-n type inversion of Si conductivity.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Multiconfiguration Dirac-Fock calculations in open-shell atoms: Convergence methods and satellite spectra of the copper K{alpha} photoemission spectrum

The copper K{alpha} photoemission spectra is one of the most widely studied. Recent Dirac-Fock calculations have produced transition energies in good agreement with experiment, though they have relied on approximations that may not be transferable to other complex atoms in which uncertainties in theoretical results are dominated by poor convergence. Through a detailed examination of convergence issues in the copper spectrum, we consider the accuracy obtainable with the multiconfiguration Dirac-Fock (MCDF) method, provide the first determination of fine structure contributions to the spectrum, and demonstrate reliable techniques for modeling spectator states with vacancies in the 3p, 3d, and 4s shells.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2010

Room temperature ferromagnetism in Mn, Ni and Co ions doped Cu{sub 2}O nanorods

Here we report the synthesis and characterization of Cu{sub 2}O nanorods doped with Mn, Ni and Co transition metal ions and the study of their magnetic properties. Synthesis of the nanorods was carried out by the modified polyol method. Powder X-ray diffraction patterns clearly showed them to be polycrystalline single phase material. They exhibited ferromagnetic behavior at room temperature, however no such behavior was observed for the reference undoped sample, which indicated that unintentionally introduced magnetic impurities were not responsible for the observed phenomenon. Ferromagnetic behavior was found to be dependent on the dopant concentration and increased consistently with its increment in the material. The total magnetic moments contribution was calculated for the dopant concentration and was found to be insignificant to account for the observed ferromagnetism, therefore it was suggested that ferromagnetism could have conjured up from the induced magnetic moment in the defects created as cation vacancies in the material. The presence of the defects was supported by the room temperature photoluminescence study which showed that intensity of the peaks was dependent on the dopant concentration and increased consistently with it. There was strong correlation between the magnitude of the photoluminescence peak and the observed ferromagnetic property in the doped samples. -- Graphical Abstract: Room temperature ferromagnetism was observed in the Cu{sub 2}O nanorods doped with Mn, Ni and Co ions. The origin seems to be the defects of cation vacancies created by the dopant ions. Display Omitted

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Synthesis and spectral characteristics of Sr{sub 2}Y{sub 8}(SiO{sub 4}){sub 6}O{sub 2}: Eu polycrystals

Spectral-luminescent characteristics of Sr{sub 2}Y{sub 8}(SiO{sub 4}){sub 6}O{sub 2}: Eu powder crystal phosphor with the apatite structure and high-intensity luminescence of Eu{sup 3+} ions have been studied. The charge state of europium in the samples has been characterized by means of X-ray L{sub 3}-adsorption spectroscopy. It was established that Eu{sup 3+} forms two types of optical centers. Besides, luminescence of Eu{sup 2+}ions was found. Reduction Eu{sup 3+}{yields}Eu{sup 2+} was considered, which may be due to V{sub Sr}{sup ||} vacancy formation in the 4f crystal lattice position and to negative charge transfer by this vacancy to two Eu{sub Y}{sup 3+} ions. Thus, in the silicate lattice there exist inhomogeneously distributed oxygen-deficient centers, which are responsible for nonradiative transfer of excitation energy to Eu{sup 3+} and Eu{sup 2+} ions. To study electron-vibrational interactions in the crystal phosphor samples, their IR and Raman spectra were examined. In the luminescence spectrum of Eu{sup 2+}, a series of low-intensity bands caused by interaction of the 4f{sup 6}5d state of Eu{sup 2+} with silicate lattice vibrations was observed. - Graphical abstract: The scheme of nonradiative transfer over of energy of excitation from oxygen vacancies to ions Eu{sup 2+} and Eu{sup 3+} in Sr{sub 2}Y{sub 8}(SiO{sub 4}){sub 6}O{sub 2}: Eu phosphors. Research Highlights: {yields}In Sr{sub 2}Y{sub 8}(SiO{sub 4}){sub 6}O{sub 2}:Eu phosphors optical centers Eu{sup 2+} and Eu{sup 3+} (two types) are formed. {yields}The 4f{sup 6}5d state of Eu{sup 2+} interacts with the lattice vibrations of Sr{sub 2}Y{sub 8}(SiO{sub 4}){sub 6}O{sub 2}:Eu. {yields}In crystal lattice Sr{sub 2}Y{sub 8} (SiO{sub 4})6O{sub 2}:Eu oxygen vacancies are formed. {yields}Oxygen vacancies nonradiatively transfer the energy of excitation to Eu{sup 2+} and Eu{sup 3+} ions. {yields}Oxygen vacancies are non-uniformly distributed in a phosphorus lattice.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Microstructure and magnetic properties of electrospun one-dimensional Al{sup 3+}-substituted SrFe{sub 12}O{sub 19} nanofibers

SrAl{sub x}Fe{sub 12-x}O{sub 19} (x=0-3.0) nanofibers with diameters about 100 nm have been prepared by electrospinning and subsequent heat treatment. With Al{sup 3+} ion content ranging from 0 to 3.0, the lattice parameters decrease due to Fe{sup 3+} ions substituted by smaller Al{sup 3+} ions and the average grain size calculated by the Scherrer's equation reduces from 65 to 37 nm. The magnetization shows a continuous reduction with the Al content and its value measured at 77 K is higher than at room temperature, which can be explained by Bloch's law. For the coercivity, its value initially increases, reaching a maximum value of 617 (298 K) and 547 kA m{sup -1} (77 K) at x=2.0, and then reduces with the Al content further increase largely arising from the substituted Al{sup 3+} ion arrangement in different interstitial sites of the strontium ferrite unit cell. -- Graphical abstract: Al{sup 3+} ions substituted strontium ferrite nanofibers have been prepared by the electrospinning with a diameter of about 100 nm and the Al{sup 3+} ion substitution has a great effect on the microstructure and magnetic property of SrAl{sub x}Fe{sub 12-x}O{sub 19} nanofibers. Display Omitted Research highlights: {yields} SrAl{sub x}Fe{sub 12-x}O{sub 19} nanofibers have been fabricated by the electrospinning. {yields} There is a relation between the Al{sup 3+} ions substitution and microstructure. {yields} The magnetic property can be tuned effectively by Al{sup 3+} ion substitution. {yields} The magnetic property is influenced by measurement temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Determining the structure of tetragonal Y{sub 2}WO{sub 6} and the site occupation of Eu{sup 3+} dopant

The compound Y{sub 2}WO{sub 6} is prepared by solid state reaction at 750 {sup o}C using sodium chloride as mineralizer. Its structure is solved by ab-initio methods from X-ray powder diffraction data. This low temperature phase of yttrium tungstate crystallizes in tetragonal space group P4/nmm (No. 129), Z=2, a=5.2596(2) A, c=8.4158(4) A. The tungsten atoms in the structure adopt an unusual [WO{sub 6}] distorted cubes coordination, connecting [YO{sub 6}] distorted cubes with oxygen vacancies at the O{sub 2} layers while other yttrium ions Y{sub 2} form [YO{sub 8}] cube coordination. Y{sup 3+} ions occupy two crystallographic sites of 2c (C{sub 4v} symmetry) and 2a (D{sub 2d} symmetry) in the Y{sub 2}WO{sub 6} host lattice. With Eu{sup 3+} ions doped, the high resolution emission spectrum of Y{sub 2}WO{sub 6}:Eu{sup 3+} suggests that Eu{sup 3+} partly substituted for Y{sup 3+} in these two sites. The result of the Rietveld structure refinement shows that the Eu{sup 3+} dopants preferentially enter the 2a site. The uniform cube coordination environment of Eu{sup 3+} ions with the identical eight Eu-O bond lengths is proposed to be responsible for the intense excitation of long wavelength ultraviolet at 466-535 nm. -- Graphical abstract: The excitation and emission spectra of Y{sub 2}WO{sub 6}:Eu{sup 3+} indicates the effect of long wavelength-excited property, which is ascribed to the cube coordination environment of Eu{sup 3+} ions with the uniform Eu-O bond length. Display Omitted Research highlights: Y{sub 2}WO{sub 6} is prepared using sodium chloride as mineralizer. The structure of the compound Y{sub 2}WO{sub 6} is solved by ab-initio methods. The site occupation of Eu{sup 3+} is determined. The cube coordination of Eu{sup 3+} ions is responsible for the long wavelength excitation.

36 MATERIALS SCIENCE↗
DOE OSTI2011

First-principles study of the electronic and magnetic properties of oxygen-deficient rutile TiO{sub 2}(1 1 0) surface

Based on first-principles electronic structure calculations we find that the bridging oxygen vacancies on the (1 1 0) surface is more favorable and may be responsible for the unexpected ferromagnetism in undoped rutile TiO{sub 2}. Our results show that the ferromagnetism largely originates from the d orbitals of low-charge-state Ti ions converted from Ti{sup 4+} ions induced by the surface oxygen vacancies. The second-nearest neighbors of these ions (fivefold coordinated Ti) also contribute to the total magnetic moments. The spins induced by the local oxygen vacancies form a ferromagnetic arrangement. -- Graphical Abstract: The study investigates the magnetic properties of the oxygen-deficient rutile TiO{sub 2}(1 1 0) surface from first principle calculations. The adjacent oxygen vacancies form a ferromagnetic arrangement due to the double exchange interaction. Display Omitted Highlights: {yields} There should be more V{sub O}'s than V{sub Ti}'s on the (1 1 0) surface layer of TiO{sub 2}. {yields} Magnetic moments induced by the isolated V{sub O} form a paramagnetic arrangement. {yields} Magnetic moments induced by the concentrated V{sub O}'s form a ferromagnetic arrangement. {yields} Double exchange is the dominant coupling mechanism of the ferromagnetism.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Benefits of Damage Engineering for PMOS Junction Stability

As CMOS devices continue to shrink, the formation of ultra shallow junction (USJ) in the source/drain extension remains to be a key challenge requiring high dopant activation, shallow dopant profile and abrupt junctions. The next generations of sub nano-CMOS devices impose a new set of challenges such as elimination of residual defects resulting in higher leakage, difficulty to control lateral diffusion, junction stability post anneal and junction formation in new materials. To address these challenges for advanced technological nodes beyond 32 nm, it is imperative to explore novel species and techniques. Molecular species such as Carborane (C{sub 2}B{sub 10}H{sub 12}), a novel doping species and a promising alternative to monomer Boron is of considerable interest due to the performance boost for 22 nm low power and high performance devices. Also, to reduce residual defects, damage engineering methodologies have generated a lot of attention as it has demonstrated significant benefits in device performance. Varian proprietary techniques to perform implants at cold temperatures (PTC II) have demonstrated lower junction leakage, enhanced activation, reduced dopant diffusion and less dopant deactivation due to the reduction of self-interstitial atoms present at the end-of-range (EOR) with low implant temperatures. In this paper, for the first time, there is a comprehensive study of the effect of implant temperature on defect engineering affecting deactivation/reactivation, and it is well established in this paper that colder the implant temperature the better it is for damage engineering with reduced EOR defects and better amorphization. The effect has been studied over a wide range of implant temperature. To understand any difference in deactivation between molecular and monomer Boron and to provide direct comparison equivalent Boron implants, co-implanted with Carbon were also studied. Implants with wide range of temperatures are implemented using PTC II. This paper will also show how damage reduction correlates with optimum junction formation and stability.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗